1. Technical Field
The present invention relates to a direct-current motor structure and more particularly to a direct-current motor structure which has a hollow rotor and a plurality of windings wound around the hollow rotor in a specific manner.
2. Description of Related Art
An electric motor, or generally referred to as a motor, serves mainly to convert the electricity received into mechanical energy and produce kinetic energy from the mechanical energy in order to drive another device. Hence, motors have been extensively used in a variety of products such as electric vehicles, lathes, electric fans, and water pumps. Generally, there are several kinds of motors, such as Direct-current (DC) motors, Alternating-Current (AC) motors, pulse motors, etc. With the advent of silicon controlled rectifiers (SCRs) and the improvement of magnetic materials, carbon brushes, and insulating materials, plus the increasing demand for variable-speed control, DC motors have once again become a crucial technology in industrial automation. This is mainly because both the “rotation speed vs. torque” and “current vs. torque” characteristic curves of DC motors are linear, which renders DC motors simple and easy to control. DC motors, therefore, remain the most common motors for variable-speed control.
Referring to FIG. 1, the structure of a conventional DC motor 1 essentially includes a housing 10, a pivot shaft 11, a rotor 12, a stator 13, and a commutator 14. The housing 10 is provided therein with a receiving space 101. The pivot shaft 11 is pivotally provided in the housing 10 and has one end formed as an output shaft 111. The output shaft 111, juts out of the housing 10. The rotor 12 is assembled from a plurality of silicon steel plates, is fixedly mounted around the pivot shaft 11, and is wound with a plurality of windings. The stator 13 is composed of permanent magnets, is fixedly provided on the inner wall of the housing 10, corresponds to the outer periphery of the rotor 12, and is spaced from the rotor 12. The commutator 14 is provided in the receiving space 101, is configured to receive external electricity, and is electrically connected to the windings in order to supply electricity to the windings. The commutator 14 can also change the direction of the current supplied to the windings. According to Fleming's left-hand rule or right-hand palm rule, a conductive wire placed in a magnetic field and supplied with a current generates a magnetic field which cuts through the existing magnetic field lines such that the conductive wire is moved. When the windings on the rotor 12 are supplied with electricity, therefore, the magnetic fields generated by the windings cut through the lines of magnetic force generated by the stator 13, producing a torque that rotates the rotor 12 and thereby converts electrical energy into kinetic energy. For example, referring to FIG. 1B, where the lines of magnetic force of the stator 13 are from left to right, a current flowing into the windings of the rotor 12 from the right and exiting to the left causes the rotor 12 to generate a torque that forces the rotor 12 into clockwise rotation.
However, the structure of the conventional DC motors, an example of which is shown in FIG. 1 and designated by the reference numeral 1, has had little innovative advancement for so long that the related industry is left with no other choice than to improve the transmission mechanisms of DC motors. The inventor of the present invention wondered whether the conventional DC motors could be improved structurally to produce a novel DC motor structure whose components (e.g., stator) can be easily adjusted in number or mounting position to suit different purposes of use, and which can hence win users' favor and secure a certain market share. The issue to be addressed by the present invention is to provide such structural improvement.